Abstract
1 Introduction
While progress towards laser-based indirect drive inertial confinement fusion (ICF) is being made[
Los Alamos National Laboratory (LANL) has adopted the strategy of increasing the case-to-capsule ratio and reducing the convergence ratio for each of its ignition campaigns as a means to achieve 1D like behavior. There are currently three major ICF campaigns under way at LANL. The first is a large case-to-capsule, low radiation temperature target design that takes advantage of beryllium capsules[
2 High case-to-capsule ratio, low radiation temperature beryllium capsule campaign
One of the goals of the Los Alamos program is evaluate the benefits of beryllium capsules compared to other ablator options such as plastic (CH) or high density carbon (HDC). During the first beryllium ablator campaign, the target design for the campaign took advantage of the hohlraum development by the high foot campaign[
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While it is known that increasing the case-to-capsule ratio (ratio of hohlraum to capsule radius) smooths the x-ray radiation pattern on the capsule, the benefits of radiation smoothing is not a strong function above a case-to-capsule ratio of
With this in mind, a series of 1D clean simulations, i.e., no mix, have been completed to evaluate the energetics in case-to-capsule ratio versus convergence ratio space as shown in Figure
For the upcoming high case-to-capsule ratio campaign, an
Given the conservative target design, we expect to produce symmetric implosions with little time dependent swings. If we do achieve a 1D like implosion, the next step will be to move towards larger capsules to determine at which case-to-capsule ratio symmetry control for beryllium capsules degrades. From those experiments, we can hydro-scale the target and get an estimate of how much energy would be needed to achieve ignition with the low radiation temperature, high case-to-capsule beryllium capsule target design.
3 Liquid layers
Liquid fuel layers are an alternative approach to control the convergence ratio[
Recent technological advances in target fabrication techniques for producing foam lined HDC capsules has made liquid layer implosions possible[
Recently, the first liquid layered target experiments were successfully fielded on NIF demonstrating the capability[
4 Double shells
Double shell targets provide a very different approach to ICF than single shells[
Unlike single shells that use a central hot spot to ignite and initiate burn of the cold dense fuel surrounding the hot spot, double shells ignite via volume ignition, i.e., heating the entire fuel volume to fusion conditions. Volume ignition with similar laser energies as for hot spot ignition is possible because of several design factors. The inner shell is made of a mid- to high-
Double shell targets have a different set of concerns than single shell targets. For double shells, the ablative physics of the outer shell, the inflight aspect ratio, pulse shaping and the fact that a fuel layer is not needed are advantages. In addition, the implosions do not require high implosion velocities. The primary trade-off is the engineering challenge of building the precision double shell targets. For double shells the other key challenges compared to single shell hot spot ignition is mix at the inner shell fuel interface and preheating of the inner shell by high energy x-rays. Mixing of high
5 Conclusions
As we continue to march towards ICF ignition, many challenges remain. Experiments have identified several issues which are in the midst of being addressed. To assist our understanding in order to mitigate these problems, to identify other potential problems, and to evaluate modeling deficiencies, it is prudent to develop target implosions that behave as near as possible to 1D simulations, i.e., ideal as possible. This means developing less stressful target designs by increasing the case-to-capsule ratio and reducing the implosion convergence. LANL has adopted three approaches in line with this strategy, a low radiation temperature beryllium target design, liquid fuel layer targets, and double shell targets. These platforms are being developed to support ignition science experiments needed to provide guidance on the most likely path towards ignition.
References
[3] H. S. Park, O. A. Hurricane, D. A. Callahan, D. T. Casey, E. L. Dewald, T. R. Dittrich, T. Doeppner, D. E. Hinkel, L. F. Berzak Hopkins, S. Le Pape, T. Ma, P. K. Patel, B. A. Remington, H. F. Robey, J. D. Salmonson, J. L. Kline. Phys. Rev. Lett., 112(2014).
[4] D. S. Clark, C. R. Weber, J. L. Milovich, J. D. Salmonson, A. L. Kritcher, S. W. Haan, B. A. Hammel, D. E. Hinkel, O. A. Hurricane, O. S. Jones, M. M. Marinak, P. K. Patel, H. F. Robey, S. M. Sepke, M. J. Edwards. Phys. Plasmas, 23(2016).
[5] S. R. Nagel, S. W. Haan, J. R. Rygg, M. Barrios, L. R. Benedetti, D. K. Bradley, J. E. Field, B. A. Hammel, N. Izumi, O. S. Jones, S. F. Khan, T. Ma, A. E. Pak, R. Tommasini, R. P. J. Town. Phys. Plasmas, 22(2015).
[7] A. N. Simakov, D. C. Wilson, S. A. Yi, J. L. Kline, D. S. Clark, J. L. Milovich, J. D. Salmonson, S. H. Batha. Phys. Plasmas, 21(2014).
[9] S. A. Yi, A. N. Simakov, D. C. Wilson, R. E. Olson, J. L. Kline, D. S. Clark, B. A. Hammel, J. L. Milovich, J. D. Salmonson, B. J. Kozioziemski, S. H. Batha. Phys. Plasmas, 21(2014).
[10] T. R. Dittrich, S. W. Haan, S. Pollaine, A. K. Burnham, G. L. Strobel. Fusion Technol., 31, 402(1997).
[13] John Lindl. Phys. Plasmas, 2, 3933(1995).
[14] J. J. MacFarlane. J. Quant. Spectrosc. Radiat. Transfer, 81, 287(2003).
[16] S. F. Khan, S. A. MacLaren, J. D. Salmonson, T. Ma, G. A. Kyrala, J. E. Pino, J. R. Rygg, J. E. Field, R. Tommasini, J. E. Ralph, D. P. Turnbull, A. J. Mackinnon, K. L. Baker, L. R. Benedetti, D. K. Bradley, P. M. Celliers, E. L. Dewald, T. R. Dittrich, L. B. Hopkins, N. Izumi, M. L. Kervin, J. L. Kline, S. R. Nagel, A. Pak, R. E. Tipton. Phys. Plasmas, 23(2016).
[17] R. E. Olson, R. J. Leeper, S. A. Yi, J. L. Kline, A. B. Zylstra, R. R. Peterson, R. Shah, T. Braun, J. Biener, B. J. Kozioziemski, J. D. Sater, M. M. Biener, A. V. Hamza, A. Nikroo, L. Berzak Hopkins, D. Ho, S. LePape, N. B. Meezan. J. Phys.: Conf. Ser., 717(2016).
[18] R. E. Olson, R. J. Leeper. Phys. Plasmas, 20(2013).
[23] R. E. Olson, R. J. Leeper, J. L. Kline, A. B. Zylstra, S. A. Yi, J. Biener, T. Braun, B. J. Kozioziemski, J. D. Sater, P. A. Bradley, R. R. Peterson, B. M. Haines, L. Yin, L. F. Berzak Hopkins, N. B. Meezan, C. Walters, M. M. Biener, C. Kong, J. W. Crippen, G. A. Kyrala, R. C. Shah, H. W. Herrmann, D. C. Wilson, A. V. Hamza, A. Nikroo, S. H. Batha. Phys. Rev. Lett.(2016).
[26] J. L. Milovich, P. Amendt, M. Marinak, H. Robey. Phys. Plasmas, 11, 1552(2004).
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